Software

With the small screen, this is not the best phone for video watching, or web browsing experiences

Only 16GB of memory may become limiting if you tend to install a lot of apps/games, or store a lot of videos on your phone

Performance

Excellent, top-shelf performance and reliability across the board

Camera

Just like the iPhone 6S, the primary camera is superlative, and among the very best cameras put on a phone

The front camera is underwhelming at just 1.2MP

Audio

Comes with best-in-class earphones

Loudspeaker is not deep enough

Battery

Excellent battery life (better than any other iPhone to date)

More

Packs nearly every worthwhile feature (processor, great camera, always-on Siri) from iPhone 6S into a smaller, much more compact 4-inch phone - this a great choice for Apple fans who like smaller phones

Currently this is a phone in a class of its own: there is no other phone of such size that's even remotely as powerful

The iPhone SE works with all the old iPhone 5/5S cases and accessories, too